On account of their desired mobility, vehicles customarily require self-sufficient supply means in order to furnish electric power, independently of the outside, for the onboard electric consumer systems, i.e. for ohmic consumer systems.
At present it is customary for aircraft to furnish the power required by electric onboard systems with the aid of an auxiliary power unit (APU) while on the ground. In flight operation, this is predominantly achieved with the aid of generators integrated in the engines of the aircraft.
Solar-driven aircraft have already been developed, built, and flown. A good overview in this regard may be found in Hannes Ross et al., in “Solarangetriebene Flugzeuge=The True All Electric Aircraft, Eine Übersicht”, published on the CD-ROM of the DGLR for “Deutscher Luft- and Raumfahrtkongress 2007, Frist CEAS European Air and Space Conference, Century Perspectives, 10-13 Sep. 2007” in Berlin and available in the Internet at http://hamburg.dglr.de. In the known solar planes, the current generated by solar cells on the airfoils is utilized for driving the aircraft. This does not give rise to the question of an alternative use of the solar current in the form of energy management.
In principle, solar cells on an aircraft might be utilized in addition to or as a substitute for the aircraft's APU. For example, owing to local noise and exhaust gas regulations, the use of the APU on the ground is partly restricted. In such cases the demand of electric power is hitherto being met by means of a ground power unit (GPU) or air starter unit (ASU) that is present externally of the aircraft. A GPU or an ASU is moreover employed when the battery in the APU of the aircraft is exhausted so that it is not possible to start the APU of the aircraft.
In the case of aircraft that are to meet a particular requirement profile of the ETOPS (Extended-range Twin-engine Operation Performance Standard) it is mandatory for certain flight routes to add on the APU in flight operation so as to ensure a sufficient supply of electric current for the case that an engine and thus the generators integrated therein should fail. Here, too, the APU might possibly be substituted or supported by a solar generator.
When an aircraft having left the parking position still has to wait on a taxiway of an airport for an extended time period because the runway is closed, e.g. due to an incident, it is frequently necessary particularly in the case of long-haul aircraft to request a GPU as well as an air conditioning truck, for without the power supply from the generators driven by the running engines it is not possible to guarantee sufficient air conditioning of the aircraft's cabin. Here, too, the energy balance of the aircraft might be assisted by solar energy.
However, the amount of power that may be furnished on the part of the solar cells is directly dependent on the actual irradiation intensity. It is therefore not possible, even in the case of long-haul aircraft having large outer surfaces for arranging solar cells, to always warrant that a sufficient amount of solar current may be generated. It is therefore of interest to utilize the power available from respective solar cells with as little loss as possible.